1. Field of the Invention
The present invention relates to a scroll pump that includes plate scrolls having nested scroll blades, and a tip seal that provides a seal between the tip of the scroll blade of one of the plate scrolls and the plate of the other plate scroll. The present invention also relates to a multi-stage dry type of scroll pump in which an orbiting plate scroll of the pump has scroll blades at both sides thereof.
2. Description of the Related Art
A scroll pump is a type of pump that includes a stationary plate scroll having a spiral stationary scroll blade, and an orbiting plate scroll having a spiral orbiting scroll blade. The stationary and orbiting scroll blades are nested with a clearance and predetermined relative angular positioning such that a pocket (or pockets) is delimited by and between the scroll blades. The scroll pump also has a frame to which the stationary plate scroll is fixed and an eccentric drive mechanism supported by the frame. These parts generally make up an assembly that may be referred to as a pump head (assembly) of the scroll pump.
The orbiting scroll plate and hence, the orbiting scroll blade, is coupled to and driven by the eccentric driving mechanism so as to orbit about a longitudinal axis of the pump passing through the axial center of the stationary scroll blade. The volume of the pocket(s) delimited by the scroll blades of the pump is varied as the orbiting scroll blade moves relative to the stationary scroll blade. The orbiting motion of the orbiting scroll blade also causes the pocket(s) to move within the pump head assembly such that the pocket(s) is selectively placed in open communication with an inlet and outlet of the scroll pump.
In an example of such a scroll pump, the motion of the orbiting scroll blade relative to the stationary scroll blade causes a pocket sealed off from the outlet of the pump and in open communication with the inlet of the pump to expand. Accordingly, fluid is drawn into the pocket through the inlet. Then the pocket is moved to a position at which it is sealed off from the inlet of the pump and is in open communication with the outlet of the pump, and at the same time the pocket is collapsed. Thus, the fluid in the pocket is compressed and thereby discharged through the outlet of the pump. The sidewall surfaces of the stationary orbiting scroll blades need not contact each other to form a satisfactory pocket(s). Rather, a minute clearance may be maintained between the sidewall surfaces at the ends of the pocket(s).
Oil may be used to create a seal between the stationary and orbiting plate scroll blades, i.e., to form a seal(s) that delimits the pocket(s) with the scroll blades. On the other hand, certain types of scroll pumps, referred to as “dry” scroll pumps, avoid the use of oil because oil may contaminate the fluid being worked by the pump. Instead of oil, dry scroll pumps employ a tip seal or seals each seated in a groove extending in and along the length of the tip (axial end) of a respective one of the scroll blades (the groove thus also having the form of a spiral). More specifically, each tip seal is provided between the tip of the scroll blade of a respective one of the plate scrolls and the plate of the other of the plate scrolls, to create a seal which maintains the pocket(s) between the stationary and orbiting scroll blades. Such tip seals may wear out over time and thus, require periodic replacement.
A scroll pump as described above may be of a vacuum type, in which case the inlet of the pump is connected to a chamber that is to be evacuated. Conversely, the scroll pump may be of a compressor type, in which case the outlet of the pump is connected to a chamber that is to be supplied with fluid by the pump.
Furthermore, a scroll pump may also be configured as a multi-stage type to provide multiple stages of compression and/or to provide a greater capacity (displacement) for the pump. To this end, a scroll pump may have two stationary plate scrolls and an orbiting plate scroll interposed between the stationary plate scrolls. The orbiting plate scroll has a plate, and orbiting scroll blades projecting from both sides of the plate, respectively. Each of the orbiting scroll blades is nested with the stationary scroll blade of a respective one of the stationary plate scrolls. Therefore, several tip seals may be provided in a dry type of multi-stage scroll pump.